1. Field of the Invention
The present invention relates to an image pickup device, and more particularly, to a high-speed image pickup method and controller for a solid-state charge coupled device (CCD) type image pickup device and for a complementary metal-oxide-silicon (CMOS) image sensor.
2. Description of the Related Art
When an image which is too bright is picked up by a camera, the output image is saturated with a large amount of incident light so that a desirable output image cannot be obtained. To prevent this problem, the exposure of a camera is adjusted to control the amount of incident light in a camera system. One of the methods used to adjust the exposure is a high-speed image pickup. The high-speed image pickup is a method of controlling the amount of incident light by reducing the time during which charge accumulates at each pixel in a CCD or CMOS image sensor.
The principle of operation of a CCD according to a high-speed image pickup method will be described. The pixels of the CCD are photosensitive so that they have a voltage proportional to the intensity of light. A vertical transmitting signal applied to the CCD has two functions. The first one is to simultaneously transmit charges accumulated at each pixel of the CCD to a vertical transmission register. The second one is to store a charge signal transmitted to the vertical transmission register in a horizontal transmission register. The first function is performed once throughout a single image at an initial stage, and the second function is performed on every horizontal line.
When a vertical transmission signal is applied to a CCD in the form of a field transmission signal, charges accumulated at each pixel are simultaneously transmitted to a vertical transmission register. In other words, the voltage values of the pixels corresponding to a single image are simultaneously transmitted to the vertical transmission register. Accordingly, the vertical transmission register has single horizontal line image information in a horizontal direction.
When a vertical transmission signal is applied to a CCD in the form of a line transmission signal, charge signals corresponding to individual horizontal lines in an image are sequentially transmitted to a horizontal transmission register starting from a horizontal line at the top of the image. Charge signals corresponding to a single horizontal line are output pixel by pixel in response to a horizontal transmission signal. When a single horizontal line is completely output with such an operation, another vertical transmission signal is applied in the form of a line transmission signal, the next horizontal line is transmitted to the horizontal transmission register, and a horizontal transmission signal is output, thereby outputting pixels one by one. By repeating this process, the pixels of an image are output one by one from the top left to the bottom right.
In the conventional technology, a special high-speed image pickup device is used to adjust a charge accumulation time of an image pickup device such as a CMOS image sensor or to achieve the high-speed image pickup of a CCD. To realize such a high-speed image pickup device, a highly sensitive material should be used. In addition, it is difficult to realize a circuit for reading an image picked up at high speed. Moreover, the special high-speed image pickup device incurs high expense, which is a limitation in making a low price camera system such as a PC (personal computer) camera using a CMOS image sensor.